You may want to consider the structures of the course - for example the Part II requirement at Cambridge, which offers a great deal of flexibility in doing academic research work in biomedically relevant science areas, or even academic study in other areas (such as Management, Biological Anthropology, or the History and Philosophy of Science and Medicine). Functionally this is similar to an iBSc offered by many other universities. They also have a (semi)formal MBPhD programme for those who do particularly well in their research and academic work in the Part II and are interested in academic medicine and medical research.
Oxford is a bit more speicfic to the biomedically relevant areas for third year/part II level work, so if you're interested more in basic science/translational research (such as in biochemistry or something) then that may be slightly more limiting. The also don't have a formal MBPhD although I believe they do arrange them on an ad hoc basis from time to time. Also, Oxford students "reapply" after pre-clinical years - they have a scheme with the London unis where those who don't remain at Oxford move on to one of London clinical courses (and sometimes I think London students do their clinical course at Oxford). While I believe any who wish to stay at Oxford can, it does say "suitably qualified" so there may be cut-offs based on performance in the pre-clinical course. Cambridge you'll be guaranteed to remain at Cambridge for the duration of the course and in and around Cambridgeshire for your placements.
For the more clinical parts of the course, they'll broadly cover the same content (as set by the GMC) but are likely to vary in their focus and style, as indicated by the comment above about anatomy. I'm not too sure to what extent this varies so, you may want to carefully look into the course structures, and possibly contact the universities themselves.